Distribution with Mnesia

Serge Aleynikov serge@REDACTED
Tue Aug 12 12:50:45 CEST 2003


I wonder in case of your suggested use of the msesia's distribution 
what's the penalty of a restart of an "extra" node?  Apparently, the 
first thing such a node would do is call wait_for_table().  In my small 
experiments a call to this function on a mnesia node containing a disk 
image of a 15M table took a couple of minutes to complete (which seemed 
conciderably long, as I would think that the disk image uses binary 
format and involves no parsing).  If both primary and "extra" nodes 
reside in the same LAN, is the wait_for_table() call on the "extra" 
diskless distributed node is as slow (or even slower due to LAN speed 
vs. disk speed) than calling it on the primary node?


Ulf Wiger (ÄL2/EAB) wrote:
> Marc,
> If you want to have a very dynamic network of mnesia nodes,
> I suggest you configure a few nodes to hold a disk copy of
> the schema, and manage them with care. Then, you can connect
> other nodes using the mnesia 'extra_db_nodes' feature.
> These nodes will be "diskless" from mnesia's perspective, 
> and may come and go at will... almost. If a diskless node
> loses contact with one of the master nodes, it should 
> unconditionally restart (mnesia, at least).
> Running distributed erlang over SSL is probably a good idea.
> /Uffe
> -----Original Message-----
> From: Marc Ernst Eddy van Woerkom
> [mailto:Marc.Vanwoerkom@REDACTED]
> Sent: Tuesday, August 12, 2003 04:32
> To: erlang-questions@REDACTED
> Subject: Distribution with Mnesia
> The features of Mnesia, as described in the docs, are remarkable.
> But what exactly is its useful grade of distribution?
> Is it just usuable for a well defined group (not changing too
> much in time) of nodes that are kind of close together (e.g.
> in the same corporate LAN or WAN?
> The other extreme would be a kind of P2P setting,
> with lots nodes that join and leave the net in an 
> unpredictable fashion.
> Or not so extme:
> Would it allow connecting let's say 10 servers
> via the internet?
> Would inter node metadata flow be possible over
> encrypted channels?
> Regards,
> Marc

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